MAF sensor unplugged

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Thank you for your patience and believe me i understand exactly this last statement of your's, and the gist of it which i completely agree: "To make a diesel engine rev higher you give it more fuel to slow it down you reduce fuel" , what i'm saying based on deep theoretical study, various data logs and many kind of measurements (only from electronic point of view) is that especially in the electronic unit injector/PD engines the amount of fuel(to make it rev higher or lower) is managed by the ECU based on TP, ECT, MAP/IAT, FT and MAF inputs... what i did was to emulate a working MAF with a closely similar signal(same range 0-5V just linear from TP instead of unlinear/logarythmic from MAF) and after that hard debate on aulro i fitted a EGT gauge and realised that the EGT is higher at middle rev range(between 2000-3000rpm) with the TP input than with a perfectly working MAF input(measured at the same TP input monitored on tester, no EGR at all), also at the same TP input the MAP reading was lower and the IAT a bit higher ... so why it's that if the MAF signal is not involved in fuelling then and the combustion is the same no matter of it's input cos all i can do is to push the throttle and let the management do it's job ?
(measurements were made on the same road in the same day)
 
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I love this argument. Comes around every few months to give us a warm feeling of familiarity.
It would be nice to get a final answer
  1. because it is important
  2. because there are two strongly held, contradictory opinions
  3. because I'd really like never to have to read about it again :D
 
sierrafery said:
Thank you for your patience and believe me i understand exactly this last statement of your's, and the gist of it which i completely agree: "To make a diesel engine rev higher you give it more fuel to slow it down you reduce fuel" , what i'm saying based on deep theoretical study, various data logs and many kind of measurements (only from electronic point of view) is that especially in the electronic unit injector/PD engines the amount of fuel(to make it rev higher or lower) is managed by the ECU based on TP, ECT, MAP/IAT, FT and MAF inputs... what i did was to emulate a working MAF with a closely similar signal(same range 0-5V just linear from TP instead of unlinear/logarythmic from MAF) and after that hard debate on aulro i fitted a EGT gauge and realised that the EGT is higher at middle rev range(between 2000-3000rpm) with the TP input than with a perfectly working MAF input(measured at the same TP input monitored on tester, no EGR at all), also at the same TP input the MAP reading was lower and the IAT a bit higher ... so why it's that if the MAF signal is not involved in fuelling then and the combustion is the same no matter of it's input cos all i can do is to push the throttle and let the management do it's job ?
(measurements were made on the same road in the same day)
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On a common rail diesel engine or indeed an EDC type engine the ECU is quite capable of calculating fuel quantity without a MAF from IAT, engine temp, fuel temp and manifold pressure. It already knows how much air is being ingested for each engine speed manifold pressure and how dense it is. What it cannot do without a MAF is apply EGR to EU III regulations, because it has no way of knowing how much exhaust gas is being ingested other than the drop in airflow through the MAF sensor. Earlier EGR systems did not have a MAF but EU II regulations called for EGR with feedback for better Nox control. That is why the MAF was fitted to diesels and that is what it does, gives feedback to the ECU so that exhaust gas ingestion can be controlled. .
 
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That doesnt answer my question, in a nutshell:
i turn on the ignition, select gear and push the throttle to move, on the same road, with same ECT and FT readings at the same TP input i get different EGT and MAP(lower boost) readings with "emulated" MAF and original MAF fitted (the EGR is completely removed so no ingested exhaust gas only air)... in my limited mind the only logical explanation is that the ECU is managing the injectors differently so the amount of injected fuel is dependant on MAF input too

 
sierrafery said:
That doesnt answer my question, in a nutshell:
i turn on the ignition, select gear and push the throttle to move, on the same road, with same ECT and FT readings at the same TP input i get different EGT and MAP(lower boost) readings with "emulated" MAF and original MAF fitted (the EGR is completely removed so no ingested exhaust gas only air)... in my limited mind the only logical explanation is that the ECU is managing the injectors differently so the amount of injected fuel is dependant on MAF input too
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The MAF does NOT control fuelling. All the temperature and pressure sensors working together do that. The MAF sensor is for measuring exhaust gas ingestion on operation of EGR. MAF sensors were added to diesel engines to provide feedback on the introduction of EU level II emissions legislation. The ECU expects to see MAF readings if it does not see them it can become confused. I would think ECU for common rail is a lot more complex than that for EDC. The EDC ECU can become confused if it does not see MAF readings, i would think the common rail one suffers from this also. Perhaps your emulated MAF was not good enough and confused the ECU.
 
wammers said:
The MAF does NOT control fuelling.......... Perhaps your emulated MAF was not good enough and confused the ECU.
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At this point IMO it's worthless to continue this ''debate'' cos i think you know well how a diesel ENGINE works but not much about how an electronic EEPROM/microprocessor based MANAGEMENT with addaptive strategy and built in diagnostic protocol is conceived ... or maybe i dont understand :rolleyes:
1. a "confused" ECU should have logged an air flow related fault code(but it didnt) if the signal was not good enough and go to default where the boost is not affected(but it was), so was the EGT(exhaust gas temperature) which is affected by fuelling
2. i didnt say that the MAF controlls fuelling just that the ECU is not neglecting it's input when it comes to fuelling as long as all the other sensor inputs and driving conditions were the same but fuelling was affected only by the MAF input's amplitude while no EGR was present
 
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This thread is WAY above my head but I'll tell you what I do know. I unplugged my MAF today and took the car for a spin. Guess what? Yup, that's right. Bugger all difference.
 
Stookie42 said:
This thread is WAY above my head but I'll tell you what I do know. I unplugged my MAF today and took the car for a spin. Guess what? Yup, that's right. Bugger all difference.
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:) ... then if it ran better with it unplugged you need a new one(use only VDO), if it ran worst and you have EGR(or even if not) it's good
 
sierrafery said:
:) ... then if it ran better with it unplugged you need a new one(use only VDO), if it ran worst and you have EGR(or even if not) it's good
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On a petrol engine yes on a diesel no. Petrol engines use MAF air flow for fuelling because they are throttled by air, diesels don't they are throttled by fuel the air is constant. That is why diesel engines have more low down torque.
 
In this case it seems that reality beats the theory cos it happens on diesels too, and that's a fact prooved by real life experience corroborated with the fact that the Td5 ECU(and others too) has a air/fuel ratio calibration table in the fuel map saved in the EEPROM which is in direct relation with the injectors management, it's clearely visible with oscilloscope that the PWM signal on the injectors earth path is altered by the MAF input so there will be different amount of fuel injected based on MAF readings too...... i made this measurement on the bench while keeping all the other sensor inputs untouched, it doesnt mean that the fuelling is calculated entirely based on MAF readings like for a petrol engine just that the MAF reading is part of the algorythm and not used only for EGR by diesels as well
 
sierrafery said:
In this case it seems that reality beats the theory cos it happens on diesels too, and that's a fact prooved by real life experience corroborated with the fact that the Td5 ECU(and others too) has a air/fuel ratio calibration table in the fuel map saved in the EEPROM which is in direct relation with the injectors management, it's clearely visible with oscilloscope that the PWM signal on the injectors earth path is altered by the MAF input so there will be different amount of fuel injected based on MAF readings too...... i made this measurement on the bench while keeping all the other sensor inputs untouched, it doesnt mean that the fuelling is calculated entirely based on MAF readings like for a petrol engine just that the MAF reading is part of the algorythm and not used only for EGR by diesels as well
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What part of air is constant for any given manifold pressure do you not understand? Of course there is a MAP for varying conditions but it is not controlled by readings from MAF airflow. It is subject to RPM request, power demand, and manifold pressure. The precise quantity will vary subject to fuel temp, engine temp, IAT temp.
 
Fight!
article-2424338-0E671B0B00000578-616_634x392.jpg
 
wammers said:
What part of air is constant for any given manifold pressure do you not understand? Of course there is a MAP for varying conditions but it is not controlled by readings from MAF airflow. It is subject to RPM request, power demand, and manifold pressure. The precise quantity will vary subject to fuel temp, engine temp, IAT temp.
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What we should agree is that i'm not speaking about quantity of air in the combustion process but about how the ECU is managing the amount of injected fuel based on various sensor readings and how in reality this is affected by the MAF readings too(amongst TP, MAP/IAT, ECT, FT, AAP readings) while there is no EGR fitted.... cos that's where the "polemics" started ... you strongly sustain your statement that the MAF input on a Td5 is used for EGR nothing else explaining with irefutable arguments what happens in the combustion process while i'm trying to demonstrate that the MAF input is used in injector management too from pure electronic point of view, and even if i might not understand how a diesel ENGINE works i'm sure i understand how the electronic management is doing things... IMO that's why we'll not get to an agreement :(
 
sierrafery said:
What we should agree is that i'm not speaking about quantity of air in the combustion process but about how the ECU is managing the amount of injected fuel based on various sensor readings and how in reality this is affected by the MAF readings too(amongst TP, MAP/IAT, ECT, FT, AAP readings) while there is no EGR fitted.... cos that's where the "polemics" started ... you strongly sustain your statement that the MAF input on a Td5 is used for EGR nothing else explaining with irefutable arguments what happens in the combustion process while i'm trying to demonstrate that the MAF input is used in injector management too from pure electronic point of view, and even if i might not understand how a diesel ENGINE works i'm sure i understand how the electronic management is doing things... IMO that's why we'll not get to an agreement :(
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The airflow through the MAF does NOT effect fuelling. If it is not working then the ECU maybe effected because it expects MAF readings and is not receiving them, it may become confused and miss interpret air conditions. That is the official BMW take on it. I would think other systems working on the same principals will give similar results. Other than that the MAF airflow is only used to measure the amount of exhaust gas ingestion for EGR purposes. The ECU then modulates the EGR valve to regulate ingestion subject to conditions. Fuelling does not change in this process unless a different throttle demand power setting is requested.
 
wammers said:
... That is the official BMW take on it. I would think other systems working on the same principals will give similar results. Other than that the MAF airflow is only used to measure the amount of exhaust gas ingestion for EGR purposes.....
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i've already posted official files about BMW and Rover engines here EGR removal improvements and the VW take on it here MAF sensor unplugged ... at this stage of the discussion you are contradicting all of them too....and i presume those guys understand how a diesel engine works:cool: :(
 
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sierrafery said:
i've already posted official files about BMW and Rover engines here EGR removal improvements and the VW take on it here MAF sensor unplugged ... at this stage of the discussion you are contradicting them too. :(
Click to expand...

Look please yourself, but the airflow through the MAF does NOT control fuelling. Read up how a diesel engine works. Any incorrect signal from any sensor will cause the ECU to flip, some more than others. But flip never the less and cause running anomalies of greater or lesser extent. Early feedback systems incorporating a MAF sensor for EGR can be disabled by simply disconnecting the vacuum hose as long as you leave the MAF and modulator connected so that the ECU thinks it's still operating. Later ones are more complex and disconnecting anything may lead to shut down, sort of like an anti tamper device. As the control of diesels becomes more and more refined to cut emissions the electronic control becomes more and more complicated. But given that they still work on the same principle, a cylinder full of air and fuel added as needed to increase power and engine speed. So air is constant fuel variable, most modern common rail diesels will have a fuel air ratio of well over 100 to 1 at idle speeds.
 
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